In an image forming apparatus using an electrophotographic method such as a digital copier, a laser printer, and the like, a toner image is transferred onto a recording medium such as a recording paper and is fixed by heating and pressurizing at a predetermined condition, thereby an image is formed on the recording medium such as the recording paper. In the image forming apparatus, a condition such as a heat amount, pressure, and the like to fix the toner image is considered. Especially, in a case of forming an image at high quality, it is needed to individually set a condition for fixing the toner image depending on types of the recording medium.
An image quality for recording to the recording medium is greatly influenced by material, thickness, temperature, smoothness, a coating state, and the like. For example, regarding the smoothness, a fixing rate of toner is lower at a concave portion due to an irregularity of the recording medium depending on the condition for fixing the image. As a result, it is not possible to acquire a high quality image. That is, if the image is not fixed at a condition corresponding to the smoothness of the recording medium to which the image is formed, an irregular color or the like is caused. The high quality image is not acquired.
On the other hand, a concurrent recent development of the image forming apparatus and diversity of expressing method, there are more than several hundred types of the recording papers used as the recording medium. Moreover, a large variety of names exist depending on grammage, thickness, or the like for each type of the recording paper. Therefore, in order to form the high quality image, it is required to set a fixing condition and the like in detail based on the type, the name, and the like of the recording paper used as the recording medium.
Various types of the recording media have been marketed such as a special paper being embossed on a surface of a paper as well as a plain paper, a coated paper such as a gloss coated paper, a matt coated paper, and an art coated paper, an OHP (Over Head Projector) sheet, and the like. The types of the recording media are increased. Also, there are many types of the recording media other than the recording paper and the like.
Currently, settings such as the fixing condition and the like related to the image forming apparatus are needed to be set by a user. Thus, the user is required to have knowledge related to the various types of the recording media. Also, if the user needs to set the fixing condition, the user may feel that it is too complex to perform printing or the like. Moreover, if there is an error in the fixing condition set by the user, it is difficult to acquire the high quality image desired by the user.
Thus, technologies have been inspected, related to a sensor for identifying the recording medium such as the recording paper to automatically specify the type of the recording medium, and an image forming apparatus mounting the sensor for identifying the recording medium to automatically specify the type of the recording medium.
For the sensor for identifying the recording medium, Japanese Laid-Open Patent Application No. 2002-340518 discloses a method for detecting friction resistance of a surface by using a stylus type probe. Japanese Laid-open Patent Application No. 2003-292170 discloses a method for detecting stiffness of the recording medium by a pressure sensor or the like. Also, Japanese Laid-open Patent Application No. 2005-156380 discloses a method for imaging the surface of the recording medium by using an image pick up element such as an area sensor or the like, and specifying the type of the recording medium based on the picked up image, as a method for identifying the recording medium without contact with the recording medium.
Also, a method using a reflected light may be considered as another method for identifying the recording medium without contact. In the method using the reflected light, light emitted from a light source such as a light emitting diode (LED) or the like is emitted to the recording medium of a target to be identified, and the name or the like of the recording medium is specified based on a reflected light amount from the recording medium. The following three types of methods are presented, related to the method using the reflected light.
In a first method, as described in Japanese Laid-open Patent Application No. H10-160687, the reflected light amount is detected in a specular reflection direction of a light on a surface of the recording medium, and the name or the like of the recording medium is specified based on the reflected light amount in the specular reflection direction.
In a second method, as described in Japanese Laid-open Patent Application No. 2006-062842, multiple light amount detectors are provided to detect a amount of light reflected in the specular reflection direction of light illuminating the surface of the recording medium, to also detect a light amount of a diffuse reflection, and to identify the name or the like of the recording medium based on the detected light amount in the specular reflection direction and the light amount in the diffuse reflection direction.
In a third method, as described in Japanese Laid-open Patent Application No. H11-249353, light reflected in the specular reflection direction of light illuminating the surface of the recording medium is separated by a polarization beam splitter. Light amount of the separated light is measured and the name or the like of the recording medium is determined based on the measured light amount.
However, Japanese Laid-open Patent Application No. 2002-340518 and No. 2003-292170 disclose a contact method. Thus, there is a problem in which the surface of the recording paper or the like as the recording medium may become damaged. In Japanese Laid-open patent Application 2005-156380, it is possible to determine the smoothness or the like of the recording medium but it is difficult to determine the thickness or the like of the recording medium.
In Japanese Laid-open Patent Applications No. H10-160687, No. 2006-062842, and No. H11-249353, it is possible to roughly determine the recording medium, but it is not possible to determine the thickness or the like of the recording medium in detail. In an apparatus for determining material of a sheet member disclosed in Japanese Laid-open Patent Application No. H10-160687 and apparatuses disclosed in Japanese Laid-open Patent Application No. 2006-062842 and No. H11-249353, it is possible to identify (determine) only a non-coated paper, a coated paper, and an OHP sheet but it is not possible to specify the name of the recording medium for a high quality image formation.
In addition to the above described methods, a sensor or the like using an ultrasound or the like may be mounted to identify the recording medium in detail. By mounting multiple sensors having different schemes, a size of the image forming apparatus is increased, and also, another problem is caused such as higher costs of manufacture.
For the sensor for detecting a surface state of a printing sheet based on the reflected light amount, a semiconductor laser may be used as a light source to improve an S/N (Signal to Noise ratio). In this case, a speckle pattern may occur when a light flux illuminates a rough surface such as the surface of the printing sheet. Since the speckle pattern is different depending on portions illuminated by the light flux, dispersion of detection light at a light receiving part is caused and accuracy of identifying the printing paper may be degraded. Accordingly, the LED or the like has been generally used as the light source.